MOS transistor-based RF switch topologies for high speed capacitive tuning of oscillators

A switch circuit for a varactor matrix of a digitally controlled oscillator, comprising:

• a main switch device, comprising:
• a gate connected to a control terminal, a drain connected to a first terminal, and a source connected to a second terminal;
• a first n-channel metal-oxide semiconductor (NMOS) device, comprising:
• a gate connected to the main switch device gate, a drain connected to the first terminal, and a source connected to a ground;
• a second NMOS device, comprising:
• a gate connected to the main switch device gate, a drain connected to the second terminal, and a source connected to the ground;
• a first p-channel metal-oxide semiconductor (PMOS) device, comprising:
• a source, and a drain connected to the first terminal;
• a second PMOS device, comprising:
• a source, and a drain connected to the second terminal;
• a third PMOS device, comprising a drain connected to the source of the first PMOS device;
• and
• a fourth PMOS device, comprising a drain connected to the source of the second PMOS device.

A digitally controlled oscillator (DCO), comprising:

• an inductor;
• and
• a varactor matrix unit connected in parallel with the inductor;
• wherein:
• the varactor matrix unit comprises a first and second capacitor and a switch connected between the first and second capacitors;
• the switch comprises:
• a main switch device comprising a gate connected to a control terminal, a drain connected to a first terminal that is connected to the first capacitor, and a source connected to a second terminal that is connected to the second capacitor;
• a first n-channel metal-oxide-semiconductor (NMOS) device comprising a gate connected to the main switch device gate, a source connected to a ground, and a drain connected to the first terminal;
• a second NMOS device comprising a gate connected to the main switch device gate, a source connected to the ground, and a drain connected to the second terminal;
• and
• a pair of p-channel metal-oxide-semiconductor (PMOS) devices each comprising drains connected respectively to the first and second terminals and configured to provide a finite resistance and predefined direct current (DC) voltage to the first and second NMOS devices when an off control signal is applied to the control terminal and the main switch device and the first and second NMOS devices are each in an off state;
• and
• the inductor and varactor matrix unit are configured to produce an oscillating signal via inductance of the inductor and capacitance of the varactor matrix unit, and
• the pair of PMOS devices comprises:
• a first PMOS device, comprising:
• a gate connected to a PMOS common junction;
• a source connected to the PMOS common junction;
• and
• the drain that is connected to the first terminal;
• and
• a second PMOS device, comprising:
• a gate connected to the PMOS common junction;
• a source connected to the PMOS common junction;
• and
• the drain that is connected to the second terminal.

A method of operating a varactor matrix switch, comprising:

• receiving an off control signal defining a switch off state at a gate of a main switch device;
• turning off the main switch device in response to the off control signal;
• turning off a first n-channel metal-oxide semiconductor (NMOS) device comprising a gate connected to the main switch device gate in response to the off control signal;
• turning off a second NMOS device comprising a gate connected to the main switch device gate in response to the off control signal;
• connecting a finite resistance and predefined direct current (DC) voltage to the first NMOS device at a first terminal connection that connects a drain of the main switch device, a drain of the first NMOS device, and a drain of a first p-channel metal-oxide semiconductor (PMOS) device while the switch is in the switch off state;
• and
• connecting a finite resistance and predefined DC voltage to the second NMOS device at a second terminal connection that connects a source of the main switch device, a drain of the second NMOS device, and a drain of a second PMOS device while the switch is in the switch off state;
• wherein:
• connecting the finite resistance and predefined DC voltage to the first NMOS device comprises passing a signal received at the first terminal through the drain and a gate of the first PMOS device with the gate and a source of the first PMOS device being connected to ground;
• connecting the finite resistance and predefined DC voltage to the second NMOS device comprises passing a signal received at the second terminal through the drain and a gate of the second PMOS device with the gate and a source of the second PMOS device being connected to the ground,
• each of the gate and source of the first PMOS device is connected to a PMOS common junction, the drain of the first PMOS device is connected to the first terminal, and the PMOS common junction is connected to the ground, and
• each of the gate and source of the second PMOS device is connected to the PMOS common junction, and the drain of the second PMOS device is connected to the second terminal.